In carousel protection the first question is not rack height but container type. FM DS 8-33 Table 1 (Section 2.4, p.7) starts the decision there: with combustible bins, a carousel above 1.8 m is protected with ceiling and in-rack sprinklers together; with noncombustible containers, it is protected under DS 8-34. Get the order wrong and the whole calculation is built on the wrong footing.
The source is FM Global DS 8-33, Carousel Storage and Retrieval Systems (September 2004, Interim Revision April 2025, 18 pages). Every numerical value below is given with the data sheet's section and page number.
Three Carousel Types and Their Physical Character
Section 2.1 (p.3) covers three types: horizontal, vertical and "up and over"; Section 3.1 (p.12-14) describes their physical character.
The horizontal carousel is the most common type; most are 8 to 16 ft (2.4 to 4.9 m) high, with shelves generally less than 2 ft (0.6 m) deep. The transverse flue space is generally only about 1-1/2 in. (38 mm); by contrast, the longitudinal flue between the two long legs is 1-1/2 to 2 ft (460 to 610 mm) wide and, if not enclosed, gives good access for fixed protection (Section 3.1.1, p.13). A vertical carousel works like a Ferris wheel; each unit is small, with a footprint generally under 50 ft2 (4.6 m2) and a height under 20 ft (6 m) (Section 3.1.2, p.14).
Section 3.1.1 also records a critical fact from the field: even when open wire shelves or basket-type bins are used, the storage is usually so tight that it behaves like solid shelving. The assumption "open shelves, water gets through" does not work for carousels.
Where the Decision Starts: Container Type
Table 1 (Section 2.4, p.7) is a decision table:
| Condition | Action |
|---|---|
| Combustible open-top bins; combustible closed bins within wire shelving; storage that behaves like solid shelving with combustible bottoms; or a height and commodity class that require in-rack sprinklers per DS 8-9 | For carousels above 1.8 m, in-rack sprinklers per Section 2.4.2 and ceiling sprinklers per Section 2.4.1 |
| Carousel arrangements not listed above | Protect per DS 8-9 |
| Carousels using noncombustible containers | Protect per DS 8-34 |
Section 2.3.4 (p.6) says that on the noncombustible container side, no in-rack sprinklers are needed if one of two conditions is met: the containers have hinged lids, or the gap between the top of one container and the bottom of the container above is nominally 1 in. (25 mm) or less. In either case, a ceiling density of 0.25 gpm/ft2 (10 mm/min) over the most remote 2,000 ft2 (186 m2) is considered adequate. The reason is physical: the lid or the narrow gap lets water run down to the lower tiers and prevents water from collecting inside the containers and causing structural collapse.
For commodity classification Section 2.3.1 (p.6) refers to DS 8-1; as an example it states that where the product is handled in plastic containers, the classification should be at least unexpanded plastic. For details see the DS 8-1 commodity classification article.
Ceiling Sprinkler Design
Table 2 (Section 2.4.1, p.7) gives the ceiling water demand for carousels with combustible open or closed bins; the rows apply to any storage height. In all rows the orifice is 1/2 in. (15 mm) and the temperature rating 286°F (141°C):
| Commodity class | Single/double-row rack | Multiple-row rack |
|---|---|---|
| Class 1-2 | 6 mm/min / 186 m2 | 6 mm/min / 186 m2 |
| Class 3 | 8 mm/min / 186 m2 | 8 mm/min / 186 m2 |
| Class 4 | 10 mm/min / 186 m2 | 10 mm/min / 186 m2 |
| Expanded and unexpanded plastics | 12 mm/min / 186 m2 | 12 mm/min / 279 m2 |
The "Class 4" row reflects the data sheet's 2004 classification: in the April 2014 revision of DS 8-1, Class 4 was removed as a separate class and this commodity is treated as cartoned unexpanded plastic (CUP) (DS 8-1 Appendix B). The commodity class should be determined per the current DS 8-1. Two notes to the table shape the design. Note 1: the values assume no more than 5 ft (1.5 m) of storage above the top in-rack level; if exceeded, another in-rack level is added. Note 2: carousels can be counted as single, double or multiple-row racks according to the total depth defined by 3-1/2 ft (1.1 m) aisles between units.
The clearance rule is clear: Section 2.4.1.2 (p.7) requires at least 3 ft (0.9 m) between the ceiling sprinkler deflector and the top of storage; Section 2.3.5 (p.6) repeats the same requirement as 36 in. (915 mm). If the clearance above the carousels exceeds 20 ft (6.1 m), Section 2.4.1.3 (p.7-8) sets up a separate solution: a continuous noncombustible suspended ceiling is installed 3 to 10 ft (0.9 to 3 m) above the carousels, sprinklers are placed below it, and the suspended ceiling extends at least 2 ft (0.6 m) beyond the outermost row of sprinklers in every direction. The roof sprinklers above the suspended ceiling provide at least 6 mm/min for Class 1, and 8 mm/min for Class 2, 3, 4 and plastics, over 2,000 ft2 (186 m2), and this demand is not added to the demand below the suspended ceiling.
In-Rack Sprinklers: the Heart of the Carousel
Section 2.4.2 (p.8) places in-rack sprinklers in the longitudinal (interior) flue space in the middle of the carousel. Table 3 (p.9) gives the flows; in all rows the orifice is 1/2 or 17/32 in. (15 or 20 mm) and the temperature rating 165°F (74°C):
- Combustible open-top bins, Class 1-3. In a single-row rack with one level installed, 6 sprinklers at no less than 22 gpm (84 L/min) each; with more than one level, 10 sprinklers at 84 L/min each (5 on each of the two most remote lines). In double and multiple-row racks, 10 sprinklers at 84 L/min each.
- Combustible open-top bins, Class 4. In a single row, 8 sprinklers for one level and 14 for more than one level, each at 84 L/min; in double and multiple rows, 14 sprinklers (7 on each of the two most remote lines).
- Combustible open-top bins, plastics (expanded and unexpanded). The same numbers, but at no less than 30 gpm (114 L/min) per sprinkler.
- Combustible closed bins, Class 1-4 and unexpanded plastics. The demand is the same as for open-bin plastics; vertical spacing no more than 10 ft (3 m), horizontal spacing no more than 4 ft (1.2 m), and no staggering.
In the open-bin rows the vertical spacing is no more than 5-6 ft (1.5-1.8 m), horizontal spacing 7-8 ft (2.1-2.4 m) and the arrangement staggered; in a multi-level arrangement the stagger between levels is about 4 ft (1.2 m) (Section 2.4.2.1). Ceiling and in-rack demands are hydraulically balanced at the connection point. For the general logic of in-rack layout see the in-rack sprinkler design article.
Two special cases: Section 2.4.8.3 (p.11) says that if the interior face is enclosed, sprinklers in the interior flue will be ineffective, and moves the sprinklers to within 6 in. (150 mm) of the exterior face or into the flue between adjacent carousels. Section 2.4.9.1 (p.12) requires an additional row of sprinklers below the apogee in vertical carousels.
Smoke Vents, Separation and Mezzanines
Vents (Section 2.2.2, p.3). The protection in the data sheet assumes a building without roof vents or draft curtains. Section 2.2.2.1.1 gives the reason: fire tests have shown that automatic vents are not cost-effective and can increase sprinkler water demand. Permanent vents are arranged for manual operation only; where regulations require automatic vents, 360°F (182°C) links are used, and drop-out type vents are not used. Smoke is removed during the cooling phase through windows and doors at eave level and non-automatic exhaust systems (Section 2.2.2.2.1). For the counterpart of the same approach on warehouse roofs, see the roof slope, skylight and ventilation limits article.
Separation (Section 2.3.2, p.6). Where valuable goods are concentrated, there are two ways to limit damage to a single carousel: at least 3-1/2 ft (1.1 m) of separation between carousel faces, or separating each carousel with a partition such as light sheet metal, corrugated metal or 1/2 in. (13 mm) plywood. If the ends face other combustibles within 3-1/2 ft (1.1 m), a shutter that closes automatically on smoke detection is provided.
Mezzanines (Section 2.2.3, p.3-6). Mezzanines are recommended to be solid rather than grated. A solid mezzanine extends at least 2 ft (0.6 m) beyond the storage. Sprinklers below it are installed per Table 2, with at least 3 ft (0.9 m) between the deflector and the storage below; if this clearance is not available, Section 2.2.3.1.5 applies: sprinklers are placed in every flue and aisle at 8 to 10 ft (2.4 to 3 m) horizontal spacing, and the water demand is based on the most remote 10 sprinklers at 84 L/min each for Class 1-3, 14 sprinklers at 84 L/min for Class 4, and 14 sprinklers at 114 L/min for plastics. With a solid mezzanine, the upper and lower demands can be determined independently (Section 2.2.3.1.4); with a grated mezzanine they are required to be simultaneous and balanced (Section 2.2.3.2.4).
Hose, Detection and the Horizontal Carousel Exception
Section 2.4.5.1 (p.10) requires enough 1-1/2 in. (38 mm) hoses to reach every point of the carousel; an allowance of at least 100 gpm (380 L/min) is made for inside hose streams and 500 gpm (1,900 L/min) for combined inside and outside streams. Where there is only a single small carousel in a fire area, a combined allowance of 250 gpm (950 L/min) can be accepted; a small carousel is one occupying a floor area of 200 ft2 (19 m2) or less and not exceeding 8 ft (2.4 m) in height.
Section 2.4.4 (p.10) decides on smoke detection with Table 4: detection is not needed in an arrangement where smoke can be seen quickly, the carousel is not very sensitive to smoke or water, and a dead-man control is provided. Where detectors are used, the horizontal spacing is no more than 15 ft (4.6 m), and operation of a single detector stops carousel movement and sounds an alarm. Section 2.4.7 (p.10-11) states the expectation: the protection limits the fire to an area of about 200 to 250 ft2 (19 to 23 m2); if that is not acceptable, detection and separation bring the area down to the order of about 100 ft2 (9.5 m2).
The only real simplification is in Section 2.4.8.1 and Table 5 (p.11). If horizontal carousel storage is no more than 8 ft (2.4 m) and the building height no more than 25 ft (7.6 m), ceiling-only sprinkler protection can be accepted: for a 15 ft (4.6 m) building height, 0.60 gpm/ft2 over 3,500 ft2 (24 mm/min over 325 m2) with standard 17/32 in. (20 mm) orifice sprinklers, or 15 sprinklers at 50 psi (3.4 bar) with large-drop sprinklers; for 20 ft (6.1 m), 20 sprinklers, and for 25 ft (7.6 m), 25 sprinklers, again at 50 psi (3.4 bar) and with large-drop sprinklers only. If the limits are exceeded, the arrangement returns to Tables 2 and 3. Large-drop sprinklers are installed per DS 2-0; see the DS 2-0 installation field guide. For carousels with noncombustible containers see the DS 8-34 ASRS protection article.
Field Note
The most argued item in carousel projects is supporting the in-rack piping from the carousel steel structure. DS 8-33 does not prohibit this, but Section 2.4.3.1 (p.10) sets a condition: if the piping is supported from the racks, flexible grooved couplings are used at the connection between branch line and main. The reason is written in the data sheet: vibration of the carousel structure adversely affects the in-rack piping system. The same section asks, in 50- to 500-year earthquake zones as defined in DS 1-2, for flexible swing joints on sprinkler drops and impact barriers for sprinklers exposed to mechanical damage. Facilities that ignore this item see joints loosening and leaks over the years, and the leak often starts at an interior point nobody looks at during working hours. The second common error is skipping the container question of Table 1 and going straight to the DS 8-9 tables; that means choosing a different protection family for the same storage, and turning back at acceptance is expensive.
Checklist
- ☐ Commodity classified per DS 8-1, on product plus packaging plus container (Section 2.3.1)
- ☐ Table 1 decision table applied; for noncombustible containers, the DS 8-34 route taken (Section 2.4)
- ☐ Ceiling density and area from Table 2; sprinklers 286°F (141°C) with a 1/2 in. (15 mm) orifice
- ☐ Storage above the top in-rack level limited to 1.5 m (Table 2 Note 1)
- ☐ At least 0.9 m between ceiling deflector and storage (Sections 2.4.1.2 and 2.3.5)
- ☐ In-rack sprinkler number, flow, spacing and stagger drawn per Table 3
- ☐ Ceiling and in-rack demands balanced at the connection point (Section 2.4.2.1)
- ☐ Roof vents manually operated; for mandatory automatic vents, 182°C links and no drop-out type (Section 2.2.2.1.1)
- ☐ Solid mezzanine chosen; without clearance, the water demand of Section 2.2.3.1.5 applied
- ☐ Hose allowance added as 380 L/min inside and 1,900 L/min combined (Section 2.4.5.1)
- ☐ Smoke detection assessed with Table 4; a single detector stops the carousel (Section 2.4.4)
- ☐ If in-rack piping is supported from the racks, flexible grooved couplings and swing joints provided (Section 2.4.3)
Frequently Asked Questions
Are in-rack sprinklers always needed for carousel storage?
No. FM DS 8-33 Table 1 (Section 2.4, p.7) ties the decision to the container type. Where combustible open-top bins, or combustible closed bins within wire shelving, are used, in-rack sprinklers are recommended for carousels above 6 ft (1.8 m). Where noncombustible containers are used, the data sheet points to DS 8-34; under Section 2.3.4 (p.6), no in-rack sprinklers are needed for noncombustible containers with hinged lids, or where the gap between bins is nominally 25 mm or less, and a ceiling density of 10 mm/min over 186 m2 is considered adequate.
Can roof smoke vents be used above carousels?
DS 8-33 Section 2.2.2 (p.3) is clear: the protection in the data sheet assumes a building without roof vents or draft curtains. Based on fire tests, Section 2.2.2.1.1 states that automatic vents are not cost-effective and can increase sprinkler water demand. Where permanent vents exist they are arranged for manual operation only; if local regulations require automatic vents, 360°F (182°C) links are used, and drop-out type vents are not used.
Is it possible to avoid in-rack sprinklers in a horizontal carousel?
Yes, within a narrow exception. DS 8-33 Section 2.4.8.1 and Table 5 (p.11) allow ceiling-only protection where horizontal carousel storage is no more than 8 ft (2.4 m) and the building height no more than 25 ft (7.6 m). For a 15 ft (4.6 m) building height, either standard 17/32 in. (20 mm) orifice sprinklers at 24 mm/min over 325 m2, or large-drop sprinklers with 15 sprinklers at 50 psi (3.4 bar), are applied. For 20 and 25 ft heights there is no standard orifice option.
What damage area is expected in a carousel fire?
DS 8-33 Section 2.4.7 (p.10) states that the protection in the data sheet is expected to limit the fire to an area of about 200 to 250 ft2 (19 to 23 m2). If the unit value of the stored goods makes the loss in that area unacceptable, smoke detection is added, and with the separation of Section 2.3.2 the fire area is brought down to the order of about 100 ft2 (9.5 m2).
References
- FM Global Property Loss Prevention Data Sheet 8-33, Carousel Storage and Retrieval Systems, September 2004, Interim Revision April 2025. Sections used: 2.1 (p.3), 2.2.2 (p.3), 2.2.3 (p.3-6), 2.3.1-2.3.5 (p.6), 2.4.1 and Tables 1-2 (p.7), 2.4.2 and Table 3 (p.8-9), 2.4.3-2.4.7 and Table 4 (p.10-11), 2.4.8 and Table 5 (p.11), 2.4.9 (p.12), 3.1.1-3.1.2 (p.13-14).
- FM Global data sheet list: https://www.fmglobal.com/research-and-resources/fm-global-data-sheets
- FM Approvals approved product guide: https://www.fmapprovals.com
- Commodity classification: https://selvi.org/en/blog/fmglobal/ds-8-1-commodity-classification
- Automated storage with noncombustible containers: https://selvi.org/en/blog/fmglobal/ds-8-34-asrs-protection
- In-rack sprinkler layout: https://selvi.org/en/blog/nfpa/rack-storage-in-rack-sprinkler-design
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Download MEP Calc on the App StoreFM Global Property Loss Prevention Data Sheet 8-33, Carousel Storage and Retrieval Systems, September 2004, Interim Revision April 2025; clause, table and page references are listed under References. General information only: the current edition governs, and design must be carried out by a qualified engineer.